STUDY OF SPATIAL CORRELATION OF POINT DEFECTS IN NATURAL DIAMOND WITH BROWN COLORATION

This study is an investigation into the spatial correlation of various optical and infrared point defects in diamond with strongly zoned brown coloration, commonly known as brown graining in the gemological trade. A sample was chosen for its excellent display of brown coloration and relative lack of inclusions. The brown coloration was seen along octahedral growth zones, making angled patterns in the sample. The sample was polished with parallel faces oriented in the (1,0,0) direction. An infrared mapping microscope was used in conjunction with a photoluminescence mapping instrument to correlate defects with the areas of brown coloration. The infrared map was used to study the major diamond defects of A-aggregated and B-aggregated nitrogen in addition to the “amber center,” a group of bands in the infrared related to brown color in diamond. Cathodoluminescence images and hyperspectral mapping was taken to investigate the correlation of the brown coloration with the growth structures and CL active defects.

The brown color defect is thought to be vacancy clusters, aggregates of vacancies that tend to lie along growth zones and plastic deformation. It was expected that diamond defects that have a vacancy in the structure would correlate with the brown coloration. It was seen that the H4 (four nitrogen atoms surrounding two vacancies) and the H3 (two nitrogen atoms and vacancy) were positively correlated with the brown color. An unknown peak at 490.7 nm was observed to be correlated with the areas of reduced brown color, in contrast to most of the defects observed.